The present disclosure relates to crystal growth apparatus, and in particular, to an electrostatic levitation crystal growth apparatus.
A single crystal is a solid material in which atoms are regularly arranged. A crystal seed of several nanometers is called “crystal nucleus”. A crystal growth may refer to a process of growing the crystal nucleus (for example, to form a bulk pattern of a micrometer or larger).
A single crystal growth technology is essential for a materials industry and/or for a materials science. For example, a potassium dihydrogen phosphate (KDP) crystal is used to realize a laser beam. Also, a protein crystal is needed to synthesize a protein and to precisely analyze a structure of a protein. The KDP crystal is a nonlinear optical material, and a high-purity defect-free single crystal is required for its optical function. For the protein single crystal, a high-purity defect-free single crystal is also needed for development of a new material. However, such single crystals are needed to have a grain size ranging from several hundred micrometers to several meters.
The term ‘dissolution’ refers to a process of dissolving a solute in a liquid solution. The solution may be a mixture of solute and solvent. The solution may be divided into the solvent and the solute. The term ‘solubility’ refers to the extent in which a solute at a saturated state is dissolved in a given solvent, and typically, it refers to the maximum amount (g) of solute that can be dissolved in 100 g solvent. The solubility may depend on temperature and kinds of the solvent and solute. In most situations, the higher the temperature, the higher the solubility of a solid substance. A vapor pressure of solution may mean the pressure exerted by a vapor in a dynamic equilibrium state with its solid or liquid.
If a solvent is evaporated from a solution, the solution may become a saturated or supersaturated solution whose concentration is higher than its solubility. In the case where, in a solution having higher concentration than its solubility, the solution temperature is decreased or the solvent is evaporated, the solute may be precipitated. By the precipitation, a crystal may be formed from the solution in which crystalline solid is dissolved. In a process of forming the saturated solution, water may be used as the solvent. In a conventional aqueous solution crystal growth method, a crystal may be grown from a single crystal seed that is suspended in a bath filled with a solution. It may take a long time to grow a crystal by the aqueous solution crystal growth method.
By using the aqueous solution crystal growth method, it may be possible to obtain large size single crystals. However, a lot of time and a high-purity seed crystal are required for the aqueous solution crystal growth method.
In the meantime, if the solvent is evaporated, the solute may be precipitated from the solution contained in a container or crucible. However, the precipitated solute may hardly have the single crystal structure, because an interaction between the crucible and the solution disturbs the formation of the single crystal structure.
To grow a single crystal, it is necessary to restrain impurities from being contained in the crystal. Even when the restraint of impurity is successfully achieved, a crucible, in which aqueous solution is contained, may serve as the impurity. For example, the single crystal growth may be disturbed by the crucible, and as a result, a polycrystalline structure may be formed.
A crystal growth rate or a formation of a crystal nucleus is dependent on a supersaturation level of the aqueous solution. In the case that a crucible is used, the crucible may serve as an impurity source, and a wall of the crucible may lead to a difficulty in achieving a supersaturated state.
Accordingly, a non-contact crystal growth method, in which a crucible for containing the solvent is not used, is needed. In the non-contact crystal growth method, an aqueous solution may be levitated, and a levitated droplet may be used for the single crystal growth. The use of the levitated droplet may make it possible to effectively prevent the container serving as the impurity sources from being interacted with the solvent.